The statements in this section merely provide background information related to the present disclosure and do not constitute prior art.
Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG) have developed an improved and excellent video compression technology over existing MPEG-4 Part 2 and H.263 standards. The new standard is named H.264/AVC (Advanced Video Coding) and was released simultaneously as MPEG-4 Part 10 AVC and ITU-T Recommendation H.264. Such H.264/AVC (hereinafter referred to as ‘H.264’) uses a spatial predictive coding method, which is different from known video coding international standards such as MPEG-1, MPEG-2, MPEG-4 Part2 Visual and the like.
Known video coding methods use “intra prediction” for coefficients transformed in Discrete Cosine Transform Domain (or DCT Transform Domain) in pursuit of higher encoding efficiency, resulting in degradation of the subjective video quality at low band transmission bit rates. However, H.264 adopts an encoding method based on a spatial intra prediction in a spatial domain rather than in a transform domain.
Encoders using an encoding method based on the known spatial intra predictions predict a block to be currently encoded from information of the previously encoded and reconstructed previous blocks, encode information on just the difference of the predicted block from the current block to be encoded, and transmit the encoded information to a decoder. At the same time, the encoder may transmit parameters needed for prediction of the block to the decoder, or the encoder and decoder may be synchronized so that they may share the needed parameters for the decoder to predict the block. At the decoder, the desired block to currently decode is created and reconstructed by first predicting its neighboring blocks reproduced previously upon completing their decoding and then obtaining the sum of difference information or residual data transmitted from the encoder and the predicted neighboring block information. Then, again, when the parameters needed for the prediction are transmitted from the encoder, the decoder uses the corresponding one of the parameters in predicting the neighboring block information.
On the other hand, the known encoding method based on spatial intra prediction uses only square block modes. This is because a two-dimensional square transform, such as 4×4 transform, 8×8 transform, or the like, is used to improve the transform efficiency. However, the inventor(s) has experienced that in case of using square block modes, pixels in right and lower portions of a block are predicted from pixels which are spatially far apart, and thus the accuracy of prediction of the block is degraded.